Immune response to eating chitin linked to better health

Dietary fiber reduces the risk of metabolic disorders such as obesity. Chitin is a common type of fiber found in fungi and the exoskeletons of insects and crustaceans. It can trigger an immune response akin to an allergic reaction. Unlike most dietary fibers, chitin can be digested by mammals. But the mechanism by which this happens is unclear.

An NIH-funded research team, led by Dr. Steven Van Dyken at Washington University in St. Louis, examined how the immune and digestive systems of mice respond to eating chitin. Their findings appeared in Science on September 8, 2023.

Feeding mice a diet containing chitin caused their stomachs to expand. This triggered an immune response in the stomach and small intestine. Certain immune cells proliferated, and the signaling molecules produced by these cells increased. Similar immune cell and signaling responses also occurred in fat tissue. Of note, chitin induced these same responses in germ-free mice, which lacked gut microbes. This shows that the immune responses to dietary chitin didn’t depend on these microbes.

Chitin digestion required an enzyme called acidic mammalian chitinase (AMCase). This enzyme is made by cells in the stomach called chief cells. The researchers found AMCase activity in the stomachs of chitin-fed mice. Mice that lacked this enzyme could not digest chitin. Furthermore, production of AMCase required the immune response that chitin consumption triggered. This suggests that one role of the immune response to chitin is to boost AMCase production. This, in turn, aids in chitin digestion.

To test the metabolic effects of eating chitin, the researchers fed mice high-fat diets that contained either chitin or another fiber. In addition, some of the mice lacked the ability to produce AMCase, so they couldn’t break down chitin. All the mice ate similar amounts. However, chitin-fed mice had better insulin sensitivity than those fed the other fiber. Those who ate chitin but couldn’t break it down had the strongest immune response, gained the least weight, and had the least body fat.

These findings suggest that the immune response to chitin has benefits for metabolic health. This may be because the chief cells that produce AMCase also produce other digestive enzymes. The immune response to chitin may increase production of these as well to improve overall digestion. This process could be a potential therapeutic target for obesity or other metabolic diseases.

“Obesity is an epidemic,” Van Dyken says. “What we put into our bodies has a profound effect on our physiology and on how we metabolize food. We’re investigating ways to counteract obesity based on what we learn about how the immune system is engaged by diet.”

—by Brian Doctrow, Ph.D.